Technology related to the present invention includes a rotary joint illustrated in FIG. 4 (see, for example, Patent document 1 or 2 described in the paragraph) [0009]). FIG. 4 is a cross-sectional view of the rotary joint. The rotary joint 100 is intended to be equipped for a pipe passage of surface polishing equipment for polishing a surface of a silicon wafer. The rotary joint 100 is provided with a cylindrical joint body 101. An inner circumferential surface of the joint body 101 is rotatably fitted with a rotation body 102. At one end of the rotation body 102, a flange part 102A is provided, which is connected to an unshown polishing pad. The flange part 102A is connected such that a fluid passage for slurry 103 provided in the rotation body 102 and that in the polishing pad are communicatively connected to each other.
At an upper end part of the rotation body 102 illustrated in FIG. 4, a cap-like rotary seal ring 105 is fitted via an O-ring. The rotary seal ring 105 is provided at the center thereof with a fluid passage for slurry 103, which is communicatively connected to the fluid passage for slurry 103 in the rotation body 102, and a top surface surrounding the fluid passage for slurry 103 is provided with a sealing surface 105A. The rotary seal ring 105 is made of silicon carbide.
In a position facing to the rotary seal ring 105, a fixed seal ring 106 is provided. A cylindrical part 106A of the fixed seal ring 106 is movably fitted into an inner circumferential surface 110A of a head cover 110 provided at an end part of the joint body 101. On a top surface of the fixed seal ring 106, an opposed sealing surface 106B 1 coming into close contact with the sealing surface 105A is formed. Also, an inner circumferential surface passing through the fixed seal ring 106 forms an intermediate passage 107. The intermediate passage 107 is communicatively connected to the fluid passage for slurry 103 and a supply passage 11 to circulate fluid containing slurry. The fixed seal ring 106 is pressed toward the rotary seal ring 105 by a spring to bring the sealing surface 105A and opposed sealing surface 106B1 into close contact with each other. The fluid containing slurry passing through the intermediate passage 107 intrudes into a fitting portion between the inner circumferential surface 110A and the cylindrical part 106A over a long period of time. This causes rust on the inner circumferential surface 110A, so that a sealing state of the opposed sealing surface 106B1 of the fixed seal ring 106 operated by spring force with respect to the sealing surface 105A is deteriorated. In addition, the rotary seal ring 105 and fixed seal ring 106 constitute a first mechanical seal device 104.
Also, on an outer circumferential side of the first mechanical seal device 104, a cooling passage 109 is formed between the first mechanical seal device 104 and the joint body 101. The cooling passage 109 is communicatively connected to a cooling inlet 109A and an unshown outlet, and cooling water flowed into the cooling passage 109 from the cooling inlet 109A is returned outside from the outlet. Further, inside the cooling passage 109, the rotary seal ring 105 is fitted in the upper end part of the rotation body 102, so that the cooling water intrudes into a fitting portion between the rotation body 102 and the rotary seal ring 105. As a result, the cooling water rusts a fitting surface of the rotation body 102, so that it becomes difficult to remove the rotary seal ring 105 from the rotation body 102 when the sealing surface 105A is replaced due to wear.
Further, the joint body 101 is provided on an inner circumference thereof with a ring-like fluid passage for non-slurry 113 communicatively connected to a fluid passage port 113A. The fluid passage 113 is communicatively connected to a circulation passage 115 provided in the rotation body 102. At a connection part between the circulation passage 115 and the fluid passage for non-slurry 113, a second mechanical seal device 116 is arranged. The second mechanical seal device 116 substantially consists of third and fourth mechanical seals 117 and 118 arranged in the fluid passage for non-slurry 113. Also, if fluid such as pure water is circulated in the circulation passage 115, wear is accelerated simultaneously with heat generation because the pure water or the like has no lubrication effect on each sealing surface of the second mechanical seal device 116 as compared with industrial water or the like.
The third mechanical seal 117 substantially consists of a first rotary seal ring 117A slidably fitted into the rotation body 102 and a first fixed seal ring 117B fastened to the joint body 101. Also, the fourth mechanical seal 118 substantially consists of a second rotary seal ring 118A fitted into the rotation body 102 slidably in a shaft direction and a second fixed seal ring 118B fastened to the joint body 101. The first and second rotary seal rings 117A and 118A are pressed toward the first and second fixed seal rings 117B and 118B by repulsive force of their associated leaf springs 120 and 120, respectively.
Also, an outer circumferential surface of the rotation body 102 is provided with annular grooves, in both of which O-rings 125 and 125 are arranged, and a sleeve 121 is fitted into the outer circumferential surface of the rotation body 102 to form a first circulation passage 115A. Further, a second circulation passage 115B communicatively connected to the first circulation passage 115A is formed of a hole provided in the rotation body 102. The first and second circulation passages 115A and 115B constitute the circulation passage 115. The fluid flowed into the circulation passage 115 also intrudes into a fitting portion between the rotation body 102 and the sleeve 121 when flowing through the first circulation passage 115A. This rusts the fitting portion between the rotation body 102 and the sleeve 121 over a long period of time, and therefore makes it difficult to remove the sleeve 121 from the rotation body 102 when the second mechanical seal device 116 is replaced.    Patent document 1: FIG. 1 in Japanese published unexamined patent application No. H11-287372    Patent document 2: FIG. 1 in Japanese published unexamined patent application No. 2001-141150
As described above, when a sealing surface of a mechanical seal is worn or damaged, components attaching the mechanical seal must also be replaced. The current problem is that supply fluid intrudes between joining surfaces of the assembled components for the mechanical seal to cause rust. The rust or the like sticks the components to each other, which in turn makes it difficult to replace the components and also impossible to disassemble the mechanical seal. Further, the rust between the components flows with being mixed into the supply fluid, which also causes trouble to a precisely machined surface or the like to be processed.